ScalaJS で js.Object なクラスのインスタンスを生成して、そのLong型のフィールドを参照するとUndefinedBehaviorError

error.txt

scala.scalajs.runtime.UndefinedBehaviorError:
An undefined behavior was detected: 123 is not an instance of scala.scalajs.runtime.RuntimeLong

FooTest.scala

import org.scalatest.{ FunSpec, Matchers }
import scala.scalajs.js

@js.native
trait Foo extends js.Object {
  val sizeBytes: Long = js.native
}

object Foo {
  def apply(sizeByte: js.UndefOr[Long] = js.undefined): Foo = {
    js.Dynamic.literal.applyDynamicNamed("apply")(
      "sizeBytes" -> sizeByte.orElse(0L).map { x => x: js.Any }
    ).asInstanceOf[Foo]
  }
}

class FooTest extends FunSpec with Matchers {
  it("small") {
    val h = Foo(sizeByte = 123L)
    assert(h.sizeBytes == 123L)
  }

  it("max") {
    val h = Foo(sizeByte = Long.MaxValue)
    assert(h.sizeBytes == Long.MaxValue)
  }

}